My two favorites aren't really "valuable" in a monetary sense, but certainly interesting ..
Dad's father, my grandfather Sam, was stationed at Pearl Harbor when the Japanese attacked. He was an airplane mechanic, in the days before the Air Force. Right after the attack, he was sent back to the mainland. The one thing he brought back from Pearl Harbor was a coconut from a palm tree that had been on fire from bombs or something. It's burnt up on one side. Dad still has the coconut sitting on top of a book shelf at home.
My mom's mother, my Babci (grandmother in Polish) had one cousin, my "uncle" Eddie. He was a Navy boy in World War II and spent most of his time in the South Pacific. In August of 1945, he was sent to Japan for some reason (can't recall specifics) and went to Hiroshima. A day or two before the bomb fell. He bought a piece of art from a young woman in the middle of the town. It was made of wood, grass, leaves, and dirt from Hiroshima. She had created a sort of landscape of rolling hills. He left with the painting, and he never knew what happened to that woman but it's likely she was vaporized, he thinks. When he died, my family inherited the art. It still looks like it was just made yesterday. It's weird to hold a piece of pre-bomb Hiroshima.
Other than that, my valuables (some in a money sense, some in an interesting sense, some both) include autographs from Phillies and Eagles, old coins, fossils, first edition vinyl, first edition books, baseball cards, photos from way back (1800s- one great shot of my great-great-great grandfather, a rabbi in pre-pogrom Russia) and documents showing my family's involvement in the Revolutionary War.
And of course .. Beanie Babies